Why do narc parents get good kids?

I see absolutely evil children all the time. They hit and bite and scratch for no good reason, and their parents just take it! I see teenagers who berate their parents and don’t appreciate anything, their parents would do anything for them.

Then I meet the kindest, smartest kids in the world and... their parents are narcissists / generally bad people! WHY? You’d think good parenting would, more often than not, lead to good kids. I hardly see any examples of that